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A bnormalities related to the shoulder joint include various types of tendinitis, impingement syndromes, recurrent subluxations and dislocations, and degenerative joint disease. The etiology of the majority of these p a t h o b gies may be linked to disturbances caused from or resulting in abnormal joint kinematics. Of particular importance is the kinematic relationship between the scapula and the humerus, commonly referred to as the scapulohumeral rhythm. First discussed over 100 years ago by Cathcart (4), the scapulohumeral rhythm has continued to be frequently discussed and debated. It is generally accepted that a properly synchronized scapulohumeral rhythm is necessary for normal shoulder function. Because of the high dependence on active muscular forces for both scapulothoracic and glenohumeral joint stability and the fine control required to maintain the proper coupling or rhythm between the two, a reduction in forcegenerating potential may translate to a reduction in control or stabiliiration for certain types of joint motion. Following this premise, since fatigue is a process that affects the force-generating capacity of a muscle, one a p proach to studying the relationship

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The purpose of this investigation was to determine the difference in the intrinsic stiffness of the active plantarflexor muscles between young and elderly human females, and to determine changes in this stiffness associated with a 6-week strengthening exercise program. Intrinsic muscle stiffness was determined by measuring the resistance in the first 62 milliseconds offered by the muscle to multiple single stretch trials at 20% to 60% of maximal isometric contraction. Stiffnesses were related to pre-stretch torque (K/PST) by a linear fit. The K/PST relationship of the elderly subjects exhibited a steeper slope, indicating a greater increase in stiffness with an increase in pre-stretch torque. The effect of testing subjects at identical relative, but different absolute pre-stretch torque levels precluded definitive conclusions on possible stiffness differences between the age groups. After the strengthening exercise program, the plantarflexors showed an increase in maximum produced torque, and a decrease in stiffness as well as a decrease in the slope of the K/PST relationship.